Without limiting the scope of the invention, its background is described in connection with rotorcraft drive systems.
U.S. Pat. No. 9,126,678, issued to Ross, et al., is entitled “Spindle mounted tiltrotor pylon with fixed engine arrangement”, and teaches a rotor system for tilt rotor aircraft that comprises an engine disposed at a first fixed location on a wing member; a prop-rotor pylon mechanically coupled to the engine along a drive path, and a gearbox disposed in the drive path. The prop-rotor pylon is rotatably mounted on a spindle, and the prop-rotor pylon is configured to selectively rotate about a rotational axis of the spindle between a vertical position and a horizontal position. The gearbox comprises a rotational axis aligned with the rotational axis of the spindle.
U.S. Pat. No. 9,174,731, issued Ross, et al., entitled “Fixed engine and rotating proprotor arrangement for a tiltrotor aircraft”, and teaches a tiltrotor aircraft that includes a fuselage; a wing member having a first rib, a second rib, a first spar, second spar; and an upper wing skin; an engine disposed at a fixed location relative to the wing member; and a proprotor having a spindle gearbox, rotor mast, and a plurality of rotor blades drivable in rotation about the rotor mast, the spindle gearbox being rotatable about a conversion axis. The spindle gearbox is located above the upper wing skin of the wing member.